The invention relates to a circuit arrangement for driving an inductive load, preferably, a synchronous motor, from an energy source which, in essence, produces a DC voltage.
From DE-OS 38 30 016 a circuit arrangement is known for feeding, via a DC voltage transformation circuit, a load from an energy source that has a low output voltage. The DC voltage transformation circuit periodically takes energy from the energy source via a main switch element and leads this energy to the load with an increased supply voltage via an inductive element and a rectifier. Furthermore, the arrangement comprises a start switch element through which energy for generating the supply voltage is taken from the energy source in a start phase of the circuit arrangement. This known circuit arrangement comprises a main controller which is supplied with energy directly from the supply voltage and which periodically controls the main switch element. This main controller thus has an increased supply voltage level compared with the output voltage of the energy source. Additionally, a start controller is provided which is directly and exclusively fed by the energy source and periodically controls the start switch element. The switch periods for the start switch element are then shorter than those for the main switch element. The start controller and thus the start switch element are switched off when the supply voltage reaches a given value.
In the known circuit arrangement the start switch element and the start controller ensure that when the circuit arrangement is taken into operation first a supply voltage of the required level for the main controller is generated to make the main switch element operative prior to its operation. Once the main controller and the main switch element have started operating, they take over the generation of the supply voltage which is also used for operating the main controller.
The known circuit arrangement can be used for any load and thus also for the feeding of motors. However, it has appeared that for a certain use a further simplification of the circuit arrangement, especially as regards the starting of the circuit arrangement when sections thereof are taken into operation, is desirable.